1. Field of the Invention
The present invention relates to a semiconductor package using a solid-state imaging element, and a camera module using the semiconductor package.
2. Description of the Related Art
Recently, video cameras and digital cameras are in widespread use, and charge coupled device (CCD) type and amplification type solid-state imaging elements are used in these cameras. In particular, with the spread of portable electronic apparatuses such as cell phones, PDAs, and notebook computers, demands for decreasing the size, weight, thickness and, cost of a camera module are increasing.
An amplification type solid-state imaging element (CMOS image sensor) used as, e.g., an imaging element in a conventional compact camera module has an imaging pixel portion in which a plurality of pixels are two-dimensionally arranged in one semiconductor chip, and a peripheral circuit portion formed outside the imaging pixel portion. The amplification type solid-state imaging element has various MOS transistors for, e.g., transfer and amplification in each pixel of the imaging pixel portion. A photodiode generates signal charge by photoelectrically converting light having entered each pixel, and the transfer transistor and amplification transistor convert the signal charge into an electrical signal and amplify the signal. The signal of the pixel is then output to the peripheral circuit portion through a signal line.
A color filter for acquiring a color image is formed on the photodiode, and a microlens for efficiently concentrating light is formed on the color filter. The imaging element chip having the above arrangement is directly mounted (by COB: chip on board) on a printed circuit board made of a resin or ceramic. An electrode is connected by wire bonding, and a passive element is mounted on the surface (by SMT:surface mount technology). A lens holder including a cover lens is placed on the printed circuit board and adhered to it, thereby forming a camera module.
In this method, the mounting area is larger than the area of the imaging element, and this makes it impossible to unlimitedly increase the density (decrease the size, weight, and thickness). It is also difficult to reduce the cost because the number of constituent parts is large and the mounting process is complicated. Furthermore, it is necessary in the manufacturing process to thin the semiconductor substrate by grinding the back surface by using a grinder and divide the substrate by dicing while the light-receiving surface is exposed. This poses the problem that dust particles stick to the light-receiving surface and decrease the yield.
Recently, as a method of solving these problems, a package in which a light-transmitting member is adhered on the light-receiving surface and an electrode is extracted from the surface opposite to the light-receiving surface of a silicon substrate has been proposed (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2007-134735).
In these compact camera modules, when extracting an electrode extending through a semiconductor substrate from an electrode on the first main surface on which the photodiode and transistor are formed to the second main surface as the back surface of the semiconductor substrate, the thickness of the semiconductor substrate must be decreased to, e.g., about 100 μm in order to increase the manufacturing throughput.
In addition, to efficiently concentrate light to the photodiode, the microlens must be covered with a member having a refractive index lower than that of the formed microlens material. Therefore, a hollow structure in which the space above the microlens is filled with a gas (atmospheric-pressure or low-pressure ambient) having the lowest refractive index is often used. A transparent member is placed above the microlens with the hollow being interposed between them. This transparent member is spaced apart from the microlens by a patterned adhesive.
Unfortunately, when the hollow is formed on the imaging element including the photodiode and the semiconductor substrate is thinned, the semiconductor substrate decreases its strength and breaks in the region where the hollow is formed. Even when the semiconductor substrate does not break, it bends in the region where the hollow is formed, and this makes normal image display impossible.